That’s a known problem with this tablet, you need to update the BIOS
http://techtablets.com/2015/10/teclast-x98-pro-boot-to-bios-missing-emmc-fix-bios-update/
And while you’re at it, set IGD Turbo Boost to Disable, to avoid unexpected shutdowns (another common problem)
Read this forum, the X98 Pro has several problems and it is not ready for general use by non-technical people, you need to do several changes to mitigate the problem it has.
If you can, return it and get the X98 Plus instead.